This invention relates to a process for recovery of soluble alumina values from alumina-bearing ores, especially calcined domestic clays by simultaneous addition of an oxidizing agent and a reducing agent into an aqueous slurry of said alumina-bearing ores.
Alumina values are typically recovered from alumina-bearing ores, normally bauxite, by digesting said ores with hot aqueous sulfuric acid. Due to increased cost for imported and domestic bauxite and the limited supplies of domestic bauxite, the development of a commercial process for extracting alumina from domestic alumina-bearing ores, especially low-grade domestic clays, presents an important technological problem that has not yet been solved satisfactorily. For example, the Bureau of Mines Report of Investigations No. 6133, U.S. Department of the Interior, 1962 entitled "Methods for Producing Alumina from Clay" discloses an evaluation of five hydrochloric acid processes for producing alumina from clay. In one of these processes, calcined clay is digested with hydrochloric acid to produce a slurry containing soluble alumina values which is filtered to remove the insoluble silica residue. The filtrate containing soluble alumina values and soluble iron salts is treated with HCl gas to precipitate the soluble alumina as aluminum chloride hexahydrate while soluble iron remains in the filtrate. The aluminum chloride hydrate is calcined to form alumina.
U.S. Pat. No. 3,862,293 (Maurel et al.) describes a process for the selective recovery of alumina, iron, magnesium and alkali metal sulfates by digesting, at high temperature, alumina-bearing clays with concentrated sulfuric acid containing chlorine gas to precipitate iron and potassium sulfates and by-product HCl, which is recycled to precipitate aluminum chloride hexahydrate. In spite of these disclosures, there is still a need for a process to recover soluble alumina values from alumina-bearing ores, especially low-grade alumina domestic clays.
It is accordingly an object of this invention to provide a process to recover soluble alumina values from alumina-bearing ores. It is also an object of this invention to provide a low energy process to recover soluble alumina values from alumina-bearing ores, especially low-grade domestic clays.